Floating cushion for a piston and cylinder device



July 24, 1956 F. s. FLICK EIAL FLOATING CUSHION FOR A PISTON ANDCYLINDER DEVICE Filed Dec. 27, 1954 4 Sheets-Sheet 1 Bil!!! ll- FIE. 2

01 72 eys:

July 24, 1956 F. s. FLICK EI'AL FLOATING CUSHION FOR A PISTON ANDCYLINDER DEVICE 4 Sheets-Sheet 2 Filed D80. 27, 1954 Mb? Wk vow Nu y 4,1956 F. s. FLICK Em 2,755,775

FLOATING CUSHION FOR A PISTON AND CYLINDER DEVICE Filed Dec. 27, 1954 4Sheets-Sheet 3 CLEARANCE July 24, 1956 F. s. FLICK ETI'AL 2,755,775

FLOATING CUSHION FOR A PISTON AND CYLINDER mzvrca Filed Dec. 27, 1954 4Sheets-Sheet 4 PIES f7? 72 20 725 I ffraizczls 5F]? 6% n 82% 2 ya nitedStates Patent Office FLQATING CUSHION FOR A PISTON AND CYLINDER DEVICEFrancis S. Flick, Oak Park, and Walter J. Kudlaty, Elmhurst, Ill.,assignors to Flick-Reedy Corporation, a corporation of IllinoisApplication December 27, 1954, Serial No. 477,702

17 Claims. (Cl. 121-38) This invention relates to a piston and cylinderdevice, and more particularly to a cushion including a valve mechanismadapted to close the exhaust port of a cylinder to cushion a piston atthe end of its stroke, and adapted to be opened quickly by fluidpressure so that the piston is given rapid break-away at the start of areverse stroke.

Conventiontal piston and cylinder devices, whether of the single ordouble acting type, usually have a ball-check valve in each cylinderhead which allows or permits rapid entry of fluid pressure into thecylinder at the start of a piston stroke. Such check-valves aregenerally restrictive in size and permit only a gradual build-up ofpressure in the cylinder due to restricted flow so that the piston ismoved slowly until the piston cushion rides out of the main port in thecylinder head, at which time larger amounts of fluid under pressureenter the cylinder through the main port, causing the piston to movemore rapidly. The cushion of the present invention is constructed toprovide a rapid build-up of fluid pressure, and a consequent rapidbreak-away of a piston at th start of its stroke.

Another feature of the present invention is the provision of a plungerassembly having a'floating cushion sleeve of a size to make a close fitwith the 'end port in a cylinder head. The structure is such that theexhaust fluid flow maintains the cushion sleeve in floating conditionupon the plunger assembly, and centers the cushion sleeve with respectto both the piston rod and plunger port in the cylinder head so thatentry of the cushion sleeve into the end port eliminates the possibilityof scoring exposed surfaces on either member. The structure decreaseswear upon both close fitting surfaces, and increases the effective lifeof a piston and cylinder device.

The invention has a further feature which may be characterized as anautomatic pressure relief provided by the structure of the plungerassembly. The trapped fluid on the non-pressure side of a piston maybuild up to extremely high proportions and the structure of the presentinvention, in effect, limits the extent of such buildup.

One embodiment of the present invention is particularly useful inair-driven piston and cylinder devices. Trapped air on the non-pressureside of the piston may build up to an extremely high pressure value morerapidly than the air may escape through the normal clearances provided.In such instances, the piston may rebound at the end of its stroke. Thepresent floating cushion sleeve can be constructed to open to'port justbefore the end of a piston stroke to release the trapped air pressure,permitting the piston to smoothly'finish its stroke, and eliminating theundesirable results described above.

The primary object of the present invention is to provide an improvedvalve mechanism which will cushion a piston at the end of its stroke.

Another object is to providea valve mechanism which will slide openimmediately when fluid under pressure is admitted to the port and whilethe cushion plunger assenn bly is still in the main port to permit rapidbuild-up of operating fluid pressure in the cylinder chamber so that thepiston will break away rapidly at the start of a stroke.

Another object is to provide a cushion sleeve on a piston rod which willfunction as a valve mechanism and eliminate the necessity of ball-checkvalves and needle-valves in the piston and cylinder device.

Another object is to provide a function of automatic pressure reliefagainst build-up of trapped fluid pressure beyond a predetermined valueby the structure of the cushion plunger of the invention.

Another object is to provide a cushion sleeve which is arranged to rideclear of an exhaust port just before the end of a piston stroke allowingcomplete exhaust of trapped compressible fluid so that the piston maymove to the extreme end of its stroke without rebound.

Another object is to provide a cylinder cushion adapted to beincorporated in a conventional piston and cylinder device Withoutnecessitating any change in the structure of the cylinder head.

' A further object is to provide a floating cushion which is adapted tobe centered with respect to an end port in a cylinder head before andwhile entering the port.

The invention is illustrated in the accompanying drawings, in which:

Figure 1 is a fragmentary side elevational view of the piston andcylinder device;

Figure 2, an end elevational view of the piston and cylinder device;

Figure 3, a fragmentary sectional view taken as indicated on line 33 ofFigure 6;

Figure 4, a view similiar to Figure 3, taken as indicated on line 4-4 ofFigure 6;

Figure 5, a view similiar to Figure 3, taken as indicated on line 5-5 ofFigure '6;

Figure 6, a fragmentary sectional view of the piston and cylinderdevice;

Figure 7, a fragmentary sectional view taken as indicated on line 7-7 ofFigure 6;

Figure 8, a fragmentary sectional view of a modified form of the pistonand cylinder device showing needle valves in the cylinder head andcylinder cap;

Figure 9, a fragmentary sectional view of another modification of thepiston and cylinder device showing a relief passage in the port openingwhich permits exhaust of trapped fluid to port just before the end of apiston stroke; and

Figure 10, a sectional view taken as indicated on line 10-10 of Figure9.

In the embodiment illustrated, a high pressure cylinder, generallydesignated 15, preferably is formed with tubular cylinder walls 16having at its rear end a cylinder cap 17 provided with a central port17a and at its front end a cylinder head 18 provided with a central port18a. A plurality of tie-rods 21, each having a threaded end portion, arepassed through the cylinder cap 17 and head 18 exterior of the cylinderwall 16, and the parts of the cylinder 15 are held together by a nut 22on each of the threaded end portions. At the juncture of the front andrear ends of the cylinder walls 16 with the cylinder cap 17 and cylinderhead 18 is a pair of cylinder O-rings 19 and 20 which seal thecylinder15 against leakage.

A piston rod 23 is provided to support a piston assembly, generallydesignated 24, and two cushion plunger assemblies, generally designated25 and 26. All three of the assemblies are mounted on the free end 27 ofthe piston rod which is of smaller diameter than the rod 23.

The piston assembly is preferably of the type more particularlydescribed in the application of Francis S.

Patented July 24, 1956 Flick, Serial No. 365,657, filed July 2, i953.This assembly comprises a piston disk 29 which makes a close sliding fitwith the inner surface 30 of the cylinder wall 16, a pair of similarcup-shaped seals 31 and 32 each adjacent opposite faces of the pistondisk 29, and a pair of similar piston followers 33 and 34 which fitwithin the cup-shaped seals 31 and 32 to hold them in proper position.Small openings 35 and 36 in each of the piston followers lead from fluidcollecting channels 37 and 38 formed in the inside periphery of each ofthe cup-shaped seals 31 and 32. As is more completely explained in theaforementioned application, these openings and channels provide a readyoutlet for fluid under pressure which may have collected between thepiston followerand its cup-shaped seal so that blowing out of the sealis prevented upon rapid release of pressure from one side of thecylinder. A piston O-ring 39 may be provided to prevent leakage aboutthe piston rod between opposite sides of the piston assembly 24. 1

The plunger assembly 26 is mounted on the front side of the pistonassembly 24 and abuts the enlarged piston rod 23; As best seen inFigures 4 through 7, a cushion sleeve support or base 40, normallycircular in crosssection, makes a close sliding fit with the free end 27of the piston rod for purposes of assembly. The base 40 is provided witha plurality of lands 41 and grooves 42 running longitudinally of itsouter peripheral surface. The lands 41 provide bearing surfaces for acup-shaped cushion sleeve 43 slidably mounted thereon, the sleeve 43being of a size to enter and make a close fit with the inner surface 55of the port 18a. The lands 41 and sleeve are carefully fitted so thatthe lands both support and guide the sleeve in its limited movementrelative to the piston; The sleeve 43 has an annularly tapered leadingedge 54 which aids in centering the sleeve as it initially enters andsubstantially closes the port 1811. There is a slight clearance betweenthe sleeve 43 and the inner surface 55 so that some fluid may be meteredout even after the port is closed.

A plurality of passages 28 are formed by the longitudinal grooves 42between the cushion sleeve 43 and its base 40 to provide communicatingchannels from the port 180 to the interior of the cylinder 15 foradmitting fluid for initiating a return stroke of the piston. A spacer44 separates the base 40 from a washer 45 mounted adjacent the pistonassembly 24. As can be seen in Figure 3, the Washer 45 has a pluralityof circumferential notches 46 in its outer periphery, the purpose ofwhich will hereafter be made apparent. If

desired, the base 40 and spacer 44, or the spacer 44 and washer 45, maybe made integral.

The cushion sleeve 43 is provided at its rear end with an inwardlyextending flange 47 whose inner annular surface is spaced outwardly ofthe spacer 44 to form an annular opening 48 around the spacer 44. Theflange 47 acts as a valve means in that it is adapted to make a closefit with the rear face of the base 40 and will close the passages 28 toflow of fluid under pressure from the cylinder when in contact with thebase 40. The rear or trailing edge of the flange 47 has a beveledportion 49 so that the flange 47 will not cover the notches 46 in thewasher 45' when the flange is in its rearward position. Thus, when thecushion sleeve 43 is in the port 18:: and the flange is slid rearwardlyof the base 40, a continuous passageway for fluid is provided from port18a through the passages 28, the opening 48, the notches 46 and into thecylinder 15. In addition to controlling 'the flow of fluid through thepassages 28, the flange 47 limits the sliding movement of the cushionsleeve 43 by abutting adjacent faces of the base '40 and the washer 45.The cushion sleeve is moved by fluid pressure on either side as will beexplained.

The other plunger assembly 25 is mounted on the rear side of the pistonassembly 24 and has the same general structure as the plunger assembly26 described above.

The assembly 25 comprises a cup-shaped cushion sleeve 4311 having atapered leading edge 54a and slidably mounted upon a base 40a which inturn makes a close sliding fit with the free end 27 of the piston rod.The base 40a has a plurality of lands 41a and grooves 42a extendinglongitudinally in its outer surface, and is spaced from the pistonassembly by spacer 44a and washer 45a. Notches 46a in the Washer 45aserve as part of the passageway for fluid from the port 17a throughpassage 28a and annular opening 48a formed between flange 47a and thespacer 44a into the interior of the rear part of the cylinder 15. Theplunger assemblies and the piston as sembly are held in position uponthe piston rod 23 by a nut 51 upon threaded end 52 of the free end 27 ofthe piston rod.

The embodiment illustrated is a double acting piston and cylinderdevice, and each of the plunger assemblies 25 and 27 operates in thesame manner. Therefore, a description of the operation of one of themwill sufiice.

While the operation of the cushion assembly may vary slightly asoperating conditions are varied, its usual operation is believed to beas follows. Assuming that the piston is just beginning a stroke, andthat it is being driven to the left as shown in Fig. 6, the advancingface of the piston assembly 24 initially forces the exhaust fluid in thecylinder out through the open main port 18a. As the leading end of thecushion sleeve 43 approaches the main port 18a, the annular openingbetween the leading edge of the sleeve 43 and the end port 18a becomesmore and more constricted, and the velocity of fluid flow through thisannular opening is greatly increased. Since the cushion sleeve 43 isfloating upon its base 40, the fluid flow past the leading edge of thesleeve and through the annular opening tends to become equalized andcenters the sleeve with respect to the end port 18a and the piston rod27.

The decease in size of the annular opening between the sleeve 43 and themain port 18a causes an increase in the velocity of fluid flow throughthe annular opening, and is accompanied by a rapid build-up in fluidpressure near the advancing face of the piston assembly 24. Thisincreased pressure causes the sleeve 43 to slide and close the passages28 just before entry of the sleeve into the end port 18a. It is believedthat some amounts of fluid under pressure pass through the annularopening 48 and into the passages 28 before they are closed so thatadditional centering fluid pressures are applied to the floating'cushionsleeve 43.

In Figure 6 the piston assembly 24 is shown approaching the end of astroke. The tapered end 54 of the sleeve 43 has entered the end port 18aand the fluid has been trapped in the left end of the cylinder 15. Sincethe passages 28 havealready been closed by the flange 47, pressure onthe trapped fluid is relieved only by fluid seepage between the outersurface of the cushion sleeve 43 and the inner surface 55 defining theport 18a and the cylinder head 18. As the piston assembly continues itsmovement and the annular passage between the sleeve 43 and the surface55 lengthens, the ease with which the molecules of fluid are .meteredout is decreased. Thus the pressure in the trapped fluidis graduallybuilt up at the end of a stroke, and the pressure difference upon therear and front sides of the piston is decreased. Accordingly, the speedof the piston assembly is diminished near the end of a stroke, and themetering out of the fluid cushions the piston assembly, permitting it toglide gradually to theend of its stroke.

At the point of travel of the piston assembly which moves the cushionsleeve into the port opening in the head of the cylinder, an additionalfunction may occur. As described above, the only escape for the trappedfluid is in the clearance space between the outer diameter of thecushion sleeve and the port opening. Normally, this clearance is a totalof from .002" to .003" and with the sleeve centered, one-half of thisclearance will be on diaclearance over the support upon which it slides,ordinarily from .004" to .006" total. As the pressure of the trappedfluid increases because the volume of fluid cannot escape rapidly enoughto relieve the pressure, a pressure relieving phenomenon results. Thecushion sleeve itself may actually be compressed or shrink a slightamount, perhaps of the order of .001" so as to increase the size of theclearance between the sleeve and the port opening. This small increasein the clearance space size permits a slightly more rapid escape of thetrapped fluid from the space between the piston and the cylinder head.

The effect of the foregoing function is to automatically relieveexcessive pressures from building up in the space between the piston andthe cylinder head. The clearance built into the cushion sleeve and itssupport and between the sleeve and port opening thus can change underinfluence of the high pressures to limit the pressure to a predeterminedmaximum amount. As the sleeve moves further into the port opening, theslot through which the trapped fluid must pass is increased in lengthincreasing the resistance to flow of the trapped fluids out of thespace. In this manner, the piston may still be decelerated gradually toa soft stop at the end of its stroke. Even though the sleeve maycollapse a slight amount, it does not move against its support but willremain centered since the pressures on all sides are equal.

When it is desired to move the piston assembly rearwardly of theassembly, fluid pressure is admitted through the port 18a. This pressureimmediately flows into the passages 28, exerting a pressure on theflange 47 and moving it rearwardly of the cylinder, opening a passagefor fluid into the cylinder and permitting an immediate and rapidbuild-up of fluid pressure against the piston assembly 24 in the forwardend of the cylinder. This action of the cushion sleeve 43 and flange 47rapidly admits large volume of fluid under pressure so that the pistonassembly can immediately break away from its rest position adjacent thehead of the cylinder.

The operating cycle is then repeated with the plunger assembly 25 at therear end of the cylinder 15.

Figure 8 discloses a modified form of the piston and cylinder device inwhich adjustable needle valves 56 and 57 are provided in the cylinderhead 18 and cylinder cap 17, respectively. The needle valves may beadjusted to regulate further the cushioning of the piston assembly atthe end of a stroke. As is apparent in the drawings, the openings 58 and59 may be closed or partially opened by the needle valves in order toaccelerate or retard the rate of exhaust of fluid from the cylinder asthe piston assembly is nearing the end of its stroke.

Figures 9 and 10 disclose a further modification of the presentinvention. An annular internal relieving bore 60 is formed in the portopening to assist the piston assembly 24 in completing the last fractionof an inch of its stroke when air is used as the motive fluid. As can beseen in Figure 9, the relief bore 60 is placed so that the cushionsleeve may clear the inner edge thereof to open the trapped fluid spaceto port 53 just before the piston assembly 24 completes its full stroke.This open ing to port permits rapid exhaust of the remaining air underhigh pressure to release completely the pressure in an end of thecylinder so that the piston will smoothly finish its stroke.

The foregoing detailed description is given for clearness ofunderstanding only and no unnecessary limitations should be understoodtherefrom, for some modifications will be obvious to those skilled inthe art.

We claim:

1. A cushion for a piston and cylinder device having a central end port,comprising: a piston rod movable within the cylinder; a cushion sleeveslidable on the piston rod and positioned to enter and substantiallyclose the port near the end of a piston stroke; a flange on the cushionsleeve and cooperating abutments on the piston rod limiting slidingmovement of the sleeve relative tov the piston rod; one of saidabutments having a fluid passage between the sleeve and rod, said sleevebeing movable by pressure within the cylinder to close said flange overthe passage.

2. A cushion as specified in claim 1 wherein the said flange is on theinner end of said sleeve so that the sleeve end and flange are exposedto pressure in the end port for sliding the flange relative to thepiston rod to open said fluid passage.

3. A cushion as specified in claim 1 wherein said cushion sleeve andflange are integral with the flange extending radially inwardly on theinner end of the sleeve so as to close and open said fluid passage underaction of pressure in said cylinder and end port respectively.

4. A cushion as specified in claim 1 wherein an annular cushion supportis positioned on the piston rod for slidably supporting said sleeve,said support having a plurality of longitudinally extending peripheralgrooves forming said fluid passages.

5. A cushion as specified in claim 1 wherein the outer leading edge ofsaid cushion sleeve is tapered to guide said sleeve into the end portand said end port having a relief passage therein to exhaust trappedfluid in the cylinder into the port upon full entry of the sleeve intothe port.

6. A cushion for a piston rod and piston assembly movable in a cylinderhaving a head with a central fluid port, comprising: a cushion sleevefloatingly mounted for limited slidable movement on said piston rod andof a size to enter and make a close fit with said port; means forming apassage for fluid between said sleeve and said piston rod to permitfluid to pass from the cylinder to the port; and valve means on saidsleeve slidable to a position closing said passage when said sleeveenters said port, closing of said passage trapping fluid between thepiston assembly and the head at the end of a stroke.

7. A cushion for a piston rod and piston assembly movable in a cylinderhaving a head with a central fluid port, comprising: a cushion sleevemounted for limited slidable movement longitudinally of the piston rodand of a size to enter and make a close fit with said port; a base forsaid sleeve mounted on the piston rod, the outer surface of said basehaving a plurality of bearing surfaces on which said cushion sleeve mayslide and a plurality of passages joining said port and cylinder whenthe sleeve has entered the port, said base and cushion sleeve havingsutficient clearance to permit said sleeve to float to a centeredposition about the piston rod under influence of fluid flow about thesleeve; and fluid pressure responsive valve means slidable with thecushion sleeve and adapted to close said passages after said cushionsleeve enters the port to substantially confine fluid pressure betweensaid piston assembly as said assembly approaches said head.

8. A cushion for a piston rod and piston assembly movable in a cylinderhaving a head with a central fluid port, comprising: a cushion sleeve onthe piston rod floatingly mounted for limited slidable longitudinalmovement and of a size to enter and make a close fit with said port; anannular base for said sleeve mounted on the piston rod and spaced fromthe piston assembly, said base having a plurality of lands and grooves,the lands providing bearing surfaces for said cushion sleeve and thegrooves providing longitudinal passages permitting fluid access to thecylinder when the sleeve is in the port; and an inwardly extendingflange integral with said sleeve and positioned between said base andsaid piston assembly, said flange being slidable with said sleeve toclose said longitudinal passages when said sleeve has entered said port.

9. A cushion for a piston rod and piston assembly movable in a cylinderhaving a head with a central fluid port, comprising: a cushion sleevefloatingly mounted 7 for limited slidable movement' longitudinally ofthe piston rod, the front end of said cushion sleeve being. of a size toenter and make a close fit with said port; abase for said cushion sleevemounted on the piston rod, the outer surface of said base having aplurality of bearing surfaces on which said cushion sleeve is floatinglyand slidably mounted and a plurality of passages joining said port andcylinder when the sleeve has entered the port; and said sleeve includinga fluid pressure responsive valve portion slidable with the cushionsleeve and adapted to close said passages after said cushion sleeveenters the port to substantially confine fluid pressure between saidpiston assembly and said head to slow movement of said piston assemblyas said assembly approaches said head, the" head of the cylinder havinga relief passage in the port with said cushion sleeve being adapted toenter the portion to a position opening to port through said passagejust' before said piston assembly completes its stroke to permit exhaustof the re maining confined fluid pressure so that said piston assemblymay. slowly glide to the end of its stroke.

10. A cushion for a piston rod and piston assembly adapted forreciprocal movement in a cylinder having at its opposite ends a head anda cap member, each having a central fluid port, comprising: a pair ofsimilar cushion sleeves", each mounted for limited'slidable movement onthe piston rod on opposite sides of the'piston assembly and each adaptedto enter and make a close fit with'thefluid' port on its respective sideof the piston assembly; each cushion having means forming a passage t'orfluid between each sleeve and the piston rod; and each sleeve having avalve portion slidable therewith to close the passage between the pistonrod and its respective sleeve when the sleeve enters its respective porttrapping fluid in an end of the cylinder to slow movement of the pistonassembly as' it approaches said end of the cylinder.

11. A'check valve for apiston rod and piston assembly movable in acylinder having a head with a central fluid port, comprising: a basemember secured to the piston rod and having a" plurality of bearingsurfaces and longitudinally extending passages for fluid under pressure;and a cup-shaped cushion sleeve slidably mounted for limitedmovement'on' said bearing surfaces, the frontend of said cus'hion'sleevebeing of a size to make a close-fit-with said port so that substantiallyall exhaust fluidfrom cylinder to'port must pass through said passages,and the rear end of said cushion sleeve having auinw'ardly extendingflange slidable under exhaust fluid pressure to a position adjacent saidbase member to close said passages, said flange also being slidablerearwardly under fluid pressure from the port to permitrapidflowof fluidunder pressure to the cylinder and piston'assembly upon a-return stroke.

12-. In a-piston'and cylinder device, having a port for flow of fluidtherethrough, a check-valve for the port,- comprising: a ba'se'rnem'berhaving an outer periphery notched to" provide alternate longitudinalfluid passage grooves and bearing areas; a sleeve member slidably andfloatingly m'ountedup'on said bearing areas and closing one side ofsaidnotches to form said fluid passages;-a flange-on the sleevememberextending inwardly a suflicient distance-to close said-passageswhen the flange and basemember are in'contact, said sleeve member havinga closefit-within the port so that passage of fluid may 'bechecked'bymovement of said sleeve.

13; In a piston and cylinder device having a port for flow of fluidtherethrough, -a check valve for the port, comprising: a ba'se memberhaving a peripheral portion notched to provide alternate longitudinalfluid passage grooves and bearing areas} a sleeve member slidablymounted upon said heati g areas and closing one side of said notches toform saidfluid passages; a flange on the" sleeve" member extending fromthe sleeve 9. di'stanbetd' be aligned with and close said passages whenthe flange and' base member are in contact, the surface of the sleeveopposite said bearing areas having a closefit within the portso thatpassage of fluid may be checked by movement of said sleeve to close saidnotches.

14'. A combination cushion and valve for a piston rod and pistonassembly movable in a cylinder having ahead with a central fluid port,comprising: an elongated generally circular base member secured to thepiston rod and having a plurality of alternate longitudinally cittendinggrooves and lands in its outer surface; an an nular spacer memberadjacent the rear fa'ceof the base member, said spacer member having anoutside diatti-' eter smaller than the diameter of said base member; acircumferentially notched washer separating said spacer member from thepiston assembly; and a cup-shaped cushion sleeveof uniform outsidediameter floatingly' mounted for slid'able' movement on said lands ofthe? base member and of a size to enter and make a close fit with saidport, the rear end of said cushion sleeve having. an inwardly extendingflange having an inside diameter greater than the diameter of saidspacer to form an annular opening" about said spacer, said flange makinga closefit' with the rear face of said base memher under fluid pressurefrom the cylinder to close said grooves to fluid passage when saidcushion sleeve enters said port, andsaid flangebeing slidable rearwardlyun der fluid pressure from the port to permit said fluid pressure toflow from port, through said grooves, said annular opening, and saidnotches in said washer mm the cylinder. I

15 A cuShionf'or a piston and cylinder device operated by fluid underpressurea'nd having a central end port, comprising: a piston ma movableWithin'thc cylinder; a cushion sleeve floatin'gly and'slidably mountedfor limited longitudinalmovement on thepisto'n rod and adapted to enterand substantially close said port near the end of a piston stroke; andmeans forming a passage for fluid be tween the sleeve and piston rod,said fluid flowing through said means as said sleeve approaches the endport to cen-' ter said sleeve in-floa'tingcondition for entry into theend port.

16. A cushion fora pistonand cylinder device operated byfluidunder'pressure and having a central end port, comprising: a' pistonrod movable within the cylinder; a cushion sleeve floatinglyand'slidably mounted for limited longitudinal movement on" the pistonrod and adaptedto'enter and substantially close said port near the endofa piston'strolte; a base on the rod having outer surfaces supportingsaidsleeve for said limited movement, said 'baseandsl'eeve beingprovided with clearance to per mit flb'atin'g'of the sleeve 'to'acentered position about the rod.

17. A" cushion as specified in claim 16 wherein the clearan'ce betweenthe sleeve and its support permits the sleeve to float clear'of thesupport when centered and the sleeve has 'a wall subjected to pressuretrapped in the cylinder to slightlyshrinlc the sleeve'increasing a spacebetween the sleeve and port asthe'sleev'e enters the port.

Sterrett Jan. 3,1950 Peterson June 14; 1955

